A motorcycle is equipped with a saddle on which a rider sits and saddlebacks or panniers behind the saddle. It is dangerous for a rider driver and a passenger to sit together on the saddle. The saddlebacks or the panniers are too small to carry lots of things, or a heavy thing.
A sidecar is designed to be attached to the motorcycle to transport the passenger or the things.
However, a conventional sidecar is kept in the upright position while the motorcycle goes around a curve. This requires the motorcycle to reduce the speed and enlarge a turning radius when it enters a curve.
The motorcycle with the conventional sidecar is required to reduce the speed when it enters a curve. Otherwise, the motorcycle with the conventional sidecar may be overturned by centrifugal force.